JP2024500106A - Manufacturing method of glass plate that reduces overall thickness variation - Google Patents

Abstract

A method of manufacturing a glass sheet includes the steps of: (a) forming a descending glass ribbon in a vertical orientation as a function of time, the glass ribbon having a first major surface and a second major surface facing generally opposite directions; (b) a step having a major surface and a core disposed between the first major surface and the second major surface; passing a glass ribbon in the vicinity, the first heating zone causing liquefaction at the first major surface while maintaining the temperature of the core below the softening temperature; c) cutting a glass sheet from the glass ribbon after the glass ribbon has moved below the first elevated temperature zone. By passing the glass ribbon in close proximity to the first heating zone, surface defects such as overall thickness variations and surface roughness of the glass ribbon are reduced.

Description

Cross-reference of related applications

This application claims priority benefit under 35 U.S.C. 119 of U.S. Provisional Patent Application No. 63/127,330, filed December 18, 2020, and all The disclosure is hereby incorporated by reference.

The present disclosure relates to glass sheets having acceptable overall thickness variations, and further relates to glass sheets from glass ribbons having reduced thickness variations by passing the glass ribbon in close proximity to one or more elevated temperature zones. The present invention relates to a method of manufacturing glass sheets having acceptable overall thickness variations by cutting the glass sheets into pieces.

Augmented reality systems add computer-generated imagery to the real-world visual scene viewed by the user of the system. Typically, an augmented reality system adds a computer-generated image to a directly visible real-world object or scene, and may include an optical system configured to allow this object or scene to be viewed. . The optical system can utilize a light guide, which can be made of high refractive index glass, to project the computer-generated image into the user's field of view. If there are variations in the shape of the light guide, the quality of images guided by the light guide and displayed to the user may deteriorate. For example, in order to be able to output high-quality images, it is necessary to minimize the total thickness variation of the light guide.

One process to achieve a light guide with acceptable overall thickness variation is to cast a boule of high index glass, saw cut the boule into a number of wafers, and lap and polish the wafers. There are processes for planarizing the wafer by polishing or reheating the wafer. However, this process is costly and time consuming. Furthermore, reheating the wafer may cause devitrification of the glass.

Furthermore, since the liquidus viscosity of a glass composition with a high refractive index is very low (for example, 1 to 100 poise), the fusion process cannot be applied to a glass composition with a high refractive index.

Prior to this disclosure, attempts were made to form high refractive index glass sheets using a down-draw ribbon forming process. In the down-draw ribbon forming process, molten glass is introduced into a compact (such as a nip between opposing rollers). Next, the molten glass is drawn downward to form a glass ribbon. The glass ribbon is then stretched downward to attenuate (ie, reduce the thickness of the glass ribbon). Then, when the glass ribbon cools, glass sheets are successively cut from the ribbon. The down-draw ribbon forming process is less costly than the process described above in which wafers are formed from boules and roughened and polished.

However, a problem was discovered. The molded product caused variations in the thickness of the glass ribbon, and this variation in thickness could not be reduced by subsequent thinning of the glass ribbon. For example, in the upper region of the compact where the melt spreads, the main surface of the glass is preferentially cooled by the compact over the core of the glass, resulting in so-called "chill wrinkles" on the main surface. There will be ups and downs. It has been thought that this variation in thickness can be reduced by making the glass ribbon thinner. However, modeling and experimentation have demonstrated that thinning does not reduce thickness variation and may even worsen it.

The present disclosure addresses this problem by heat treating the glass ribbon such that liquefaction occurs on one or more major surfaces of the glass ribbon before cutting the glass sheet from the glass ribbon. By causing liquefaction on one or more major surfaces of the glass ribbon, thickness variations are reduced. This improvement allows high refractive index glass sheets to be formed more economically using a form-and-draw process.

According to a first aspect of the present disclosure, a method of manufacturing a glass sheet includes the steps of: (a) forming a descending glass ribbon as a function of time in a vertical orientation, the glass ribbon forming a glass ribbon in a generally opposite direction; (b) having a first major surface and a second major surface facing the direction of the glass ribbon; and a core disposed between the first major surface and the second major surface; passing the glass ribbon in close proximity to a first heated zone as the temperature rises, the first heated zone liquefying at the first major surface while maintaining the temperature of the core below the softening temperature; (c) removing the glass plate from the glass ribbon after the glass ribbon has moved below the first elevated temperature zone; and slicing.

According to the second aspect of the present disclosure, in step (b) of the first aspect, the viscosity of the first main surface is reduced and the overall thickness variation of the glass ribbon is reduced.

According to the third aspect of the present disclosure, in the second aspect, between step (b) and step (c), after the overall thickness variation is reduced, the temperature of the first main surface is and the temperature of the core approaches equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases.

According to a fourth aspect of the present disclosure, the method according to any one of the first to third aspects includes, before step (a), applying molten glass to a nip between a pair of opposing forming rollers. further comprising the step of sending. Further, forming the glass ribbon in the vertical direction includes rotating a pair of forming rollers to roll the molten glass fed to the nip into a glass ribbon.

According to a fifth aspect of the disclosure, the method according to any one of the first to fourth aspects comprises: after step (b) and before step (c), the glass ribbon is further including the step of pulling down.

According to a sixth aspect of the disclosure, in the fifth aspect, the step of pulling the glass ribbon with a tension roller reduces the thickness of the glass ribbon between the first major surface and the second major surface. .

According to a seventh aspect of the present disclosure, the method according to any one of the first to sixth aspects comprises: after step (b) and before step (c), and the second major surface.

According to the eighth aspect of the present disclosure, in any one of the first to seventh aspects, the first main surface of the cut glass plate has a surface roughness (R _a ) of less than 500 nm. be.

According to the ninth aspect of the present disclosure, in any one of the first to eighth aspects, the overall thickness variation of the glass plate cut from the glass ribbon is less than 5 μm.

According to the tenth aspect of the present disclosure, in any one of the first to ninth aspects, the overall thickness variation of the glass plate cut from the glass ribbon is different from that of the glass ribbon before step (b). This is less than 50% of the overall thickness variation.

According to an eleventh aspect of the present disclosure, in any one of the first to tenth aspects, the first main surface and the second main surface after step (a) and before step (b) The thickness of the glass ribbon between the main surface is 3 mm to 5 mm.

According to the twelfth aspect of the present disclosure, in any one of the first to eleventh aspects, the glass between the first main surface and the second main surface after step (b) The thickness of the ribbon is at least 1.5 mm.

According to the thirteenth aspect of the present disclosure, in any one of the first to twelfth aspects, between step (b) and step (c), the first main surface and the second main surface The thickness of the glass ribbon between the surfaces is reduced.

According to a fourteenth aspect of the present disclosure, in any one of the first to thirteenth aspects, the step of increasing the temperature of the first main surface includes directing the flame to the first main surface. include.

According to a fifteenth aspect of the present disclosure, in the fourteenth aspect, the step of directing the flame toward the first main surface is performed by a horizontally directed line burner, is narrower than the horizontal width of the glass ribbon facing the horizontally oriented line burner.

According to a sixteenth aspect of the present disclosure, in any one of the first to fifteenth aspects, the step of increasing the temperature of the first main surface is performed mainly by heat radiation. The method includes a step of causing the first main surface to face a high temperature body that transfers heat.

According to a seventeenth aspect of the present disclosure, in any one of the first to sixteenth aspects, step (b) reduces devitrification within the glass ribbon.

According to an eighteenth aspect of the present disclosure, in any one of the first to seventeenth aspects, in (i) before step (b), the viscosity of the glass ribbon is between 10 ¹⁰ poise and 10 ¹² poise. and (ii) in step (b), the viscosity of the first main surface of the glass ribbon from the first main surface to a depth of at least 100 μm in the thickness direction of the glass ribbon is reduced to 10 ⁵ poise or less. and (iii) before step (c), the viscosity of the glass ribbon bulk is increased to between 10 ⁶ poise and 10 ⁸ poise.

According to a nineteenth aspect of the present disclosure, in any one of the first to eighteenth aspects, step (b) is performed within a time period of less than 10 seconds.

According to the 20th aspect of the present disclosure, in any one of the 1st to 19th aspects, the refractive index of the glass plate for a wavelength of 589 nm to 633 nm at a temperature of 20° C. to 25° C. is 1.75 to 1.75. It is 2.5.

According to a twenty-first aspect of the disclosure, a method of manufacturing a glass sheet includes the steps of: (a) forming a descending glass ribbon as a function of time in a vertical orientation, the glass ribbon forming a glass ribbon in a generally opposite direction; (b) a step having a first major surface and a second major surface facing , and a core disposed between the first major surface and the second major surface; As the ribbon descends, (i) a first temperature increase increases the temperature of the first major surface to a temperature sufficient to cause liquefaction to occur at the first major surface while maintaining the temperature of the core below the softening temperature; (ii) passing the glass ribbon in close proximity to a second heating zone that increases the temperature of the second major surface to the liquidus temperature while maintaining the temperature of the core below the softening temperature; (c) cutting a glass plate from the glass ribbon after the glass ribbon has moved below the first temperature-raising zone and the second temperature-raising zone.

According to the twenty-second aspect of the present disclosure, in the twenty-first aspect, the first temperature-raising zone and the second temperature-raising zone are arranged to be shifted in the vertical direction.

According to the twenty-third aspect of the present disclosure, in the twenty-first aspect, the horizontal planes of the first temperature-raising zone and the second temperature-raising zone overlap each other.

According to the twenty-fourth aspect of the present disclosure, in the twenty-first or twenty-second aspect, in step (b), the viscosity of the first main surface is reduced, the viscosity of the second main surface is reduced, and the glass ribbon The overall thickness variation of is reduced.

According to a twenty-fifth aspect of the present disclosure, in any one of the twenty-first to twenty-third aspects, between step (b) and step (c), the overall thickness variation of the glass ribbon is After being reduced, the temperatures of the first major surface, second major surface, and core approach equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases.

Flowchart showing a method for manufacturing a glass plate according to an embodiment of the present disclosure According to the method shown in Fig. 1, molten glass is sent to a mold in the form of a pair of forming rollers, and a glass ribbon is formed in the vertical direction by the pair of forming rollers, and a glass plate cut from the glass ribbon and a glass plate cut from the glass ribbon are shown. Perspective view showing 3 is an elevational view showing the state of FIG. 2, in which the temperature of the core of the glass ribbon is lower than the softening temperature, and the temperature of the first main surface and the second main surface of the glass ribbon is changed to the temperature of the first main surface. and raising the temperature to a temperature sufficient to cause liquefaction of the glass ribbon on the second principal surface, and before thinning the glass ribbon, in order to reduce variations in the overall thickness of the glass ribbon and surface defects due to surface tension. , a diagram showing how a glass ribbon is passed in the immediate vicinity of a first temperature-raising zone and a second temperature-raising zone that are arranged to be shifted in the vertical direction. a first heating zone and a second heating zone arranged vertically without offset (i.e., horizontal planes extending through the glass ribbon overlap each other in the first heating zone and the second heating zone); Same view as Figure 3A, except passing the glass ribbon in close proximity to the heating zone. FIG. 3 is a side view showing the state of FIG. 2, and is a diagram showing a first temperature increasing zone and a second temperature increasing zone arranged at positions shifted in the vertical direction. FIG. 3 is a side view showing the state of FIG. 2, and is a diagram showing a first temperature increasing zone and a second temperature increasing zone that are not shifted in the vertical direction and are arranged in positions where horizontal planes overlap each other. It is an enlarged view of region V in FIGS. 4A and 4B, and is a diagram showing the thickness between the first main surface and the second main surface and the surface roughness of the first main surface. FIG. 3 is an enlarged view of region VI in FIG. 2, showing a state where the first main surface of the glass ribbon has cold wrinkles that contribute to variations in the overall thickness of the glass ribbon. 3A and 3B are perspective views of an embodiment of the first and second heating zones in FIGS. a first horizontally oriented line burner directing a flame; and a second horizontally oriented line burner directing a flame onto a second major surface of the glass ribbon to produce liquefaction on the second major surface. Diagram showing FIG. 3B is a perspective view of another embodiment of the first heating zone and the second heating zone in FIGS. 3A and 3B, in which the first main surface is heated mainly by heat radiation throughout the first heating zone. A first high-temperature body that transfers heat to cause liquefaction on the first main surface; A diagram showing a second high-temperature body that causes liquefaction on the main surface of FIG. This is a diagram related to Example 1, in which a quartz crucible containing a cubic glass was heated by a flame, and the cubic glass inside was heated by heat radiation from the quartz crucible. ) shows that the cold wrinkles on the surface of the cubic glass were removed within 90 seconds (“t=90 seconds”) 2 is an infrared image of a glass ribbon passing in close proximity to a first heating zone by a horizontally oriented line burner, according to an embodiment of the method of FIG. 1; FIG. A diagram showing how the glass ribbon descends and becomes thinner as the temperature of the first principal surface and the temperature of the core of the glass ribbon reach equilibrium and the effective viscosity of the glass ribbon decreases. 10 is a graph also related to Example 2, showing the surface quality measurement results of the glass plate cut from the glass ribbon of FIG. The first major surface of the glass plate that passed in the immediate vicinity has a smaller height difference than the second major surface of the glass plate that did not pass in the immediate vicinity of the heating zone while being part of the glass ribbon. Diagram showing that it had surface texture 3 is a graph related to a computer model of Example 3, in which the temperature of the first major surface of the glass ribbon decreases until liquefaction occurs on at least the first major surface, several seconds before the thinning coefficient of the glass ribbon begins to decrease; surface defects and overall thickness variations due to surface tension before the effective viscosity of the glass ribbon decreases enough for thinning of the glass ribbon to occur. Diagram illustrating the principle that sufficient time exists while liquefaction occurs on the first major surface to reduce This figure also relates to Example 3, and shows that before a decrease in the thickness of the glass ribbon is observed due to a decrease in the effective viscosity of the entire glass ribbon, the viscosity of the first principal surface increases due to the heat flux, and surface defects and surface tension occur. Diagram showing reduction to less than 1000 poise (i.e., 10 ³ poise), which is low enough to reduce overall thickness variation. It is a diagram related to Comparative Example 4A, showing the measured values of the surface roughness (R _a ) and surface texture of a glass plate cut from a glass ribbon that did not pass immediately near the first temperature increase zone before being cut. This is a diagram related to Example 4B, in which the glass ribbon was cut from a glass ribbon that had passed through the immediate vicinity of the first heating zone where the temperature was raised to a temperature sufficient to cause liquefaction on the first main surface of the glass ribbon before cutting. Diagram showing measured values of surface roughness (R _a ) and surface properties of a glass plate

Next, a method 10 for manufacturing the glass plate 12 will be described with reference to FIGS. 1 to 7B. Method 10 includes forming 14 a glass ribbon 16 in a vertical orientation. Glass ribbon 16 has a first major surface 18 and a second major surface 20. The first major surface 18 and the second major surface 20 face generally opposite directions. Glass ribbon 16 further has a first side edge 22 and a second side edge 24. First side edge 22 and second side edge 24 define generally opposite sides of glass ribbon 16 . "Vertically oriented" means that the first major surface 18 and the second major surface 20 form a substantially vertical plane. The glass ribbon 16 also has a thickness 26 that is the horizontal distance between the first major surface 18 and the second major surface 20. Further, the glass ribbon 16 has a width 28 that is the horizontal distance between the first side edge 22 and the second side edge 24. The thickness 26 and width 28 of the glass ribbon 16 may vary as a function of vertical position along the glass ribbon 16. Glass ribbon 16 has a composition.

The method 10 also includes the step of feeding 30 molten glass 32 into a mold 34 . The glass ribbon 16 is formed by the mold 34.

In some embodiments, the mold 34 includes a pair of opposing forming rollers 36a, 36b. In such embodiments, feeding 30 the molten glass 32 to the mold 34 includes feeding the molten glass 32 as a stream 38 to a nip 40 between a pair of forming rollers 36a, 36b. By way of example only, a stream 38 of molten glass 32 may be directed from a fishtail (slot opening) 42 to the center of nip 40 . The flow 38 is sent from above the horizontal rotation shafts 44a, 44b of the pair of forming rollers 36a, 36b. The width/length and thickness of slot opening 42 can vary widely. A stream 38 of molten glass 32 is delivered to nip 40 at a glass temperature of about 1000° C. or greater and has a viscosity on the order of 10 ¹ poise. The fed molten glass 32 forms a pool 46 of the molten glass 32 on the pair of forming rollers 36a, 36b. The pair of forming rollers 36a, 36b can be temperature controlled to have a surface temperature in the range of about 500° C. to about 600° C. or higher, depending on the composition and viscosity of the glass to be formed. Processes and devices for temperature control of the pair of forming rollers 36a, 36b are well understood in the art and will not be discussed in detail herein. In such embodiments using a pair of forming rollers 36a, 36b, forming 14 the glass ribbon 16 in a vertical orientation involves rotating the pair of forming rollers 36a, 36b as it is fed into the nip 40. The method includes a step of rolling the molten glass 32 into a glass ribbon 16. The pair of forming rollers 36a, 36b rotate inward toward the pool of molten glass, as shown by the arrows in FIG. 2, thereby flattening, thinning, and smoothing the molten glass 32 in the pool 46. Thus, the glass ribbon 16 extends vertically below the rotating shafts 44a, 44b of the pair of forming rollers 36a, 36b.

Although the glass ribbon 16 is molded using a pair of forming rollers 36a and 36b as the mold 34, this is only one example of the mold 34 and is not intended to be limiting. The method 10 encompasses any type of mold 34 that can be utilized to vertically form the glass ribbon 16 from the mold 34.

After forming, the glass ribbon 16 lowers as a function of time. In other words, mold 34 continuously forms glass ribbon 16 until the source of molten glass 32 for glass ribbon 16 is empty. For example, it may occur that a volume within the glass ribbon 16 that was at position 48a at one point in time drops as shaping of the glass ribbon 16 continues, and is at position 48b at a subsequent point in time.

The glass ribbon 16 has a core 50 (see FIG. 5). The core 50 is disposed between the first major surface 18 and the second major surface 20, and is, for example, equidistant from the first major surface 18 and the second major surface 20, and is located on the first side. It also includes a volume that is equidistant from the edge 22 and the second side edge 24. In embodiments, the core 50 is spaced from the first major surface 18 by at least 40 percent of the thickness 26 and from the second major surface 20 by at least 40 percent of the thickness 26. There is. In embodiments, the core 50 is spaced apart from the first side edge 22 by at least 40 percent of the width 28 and from the second side edge 24 by at least 40 percent of the width 28.

After forming the glass ribbon 16, the glass ribbon 16 is solidified. When the first main surface 18 and the second main surface 20 are solidified, there may be variations in the thickness 26 such as cold wrinkles 52 or the mold 34 may It solidifies with surface defects such as surface roughness. The cold wrinkles 52 are undulations caused by the main surfaces 18 and 20 being cooled more preferentially than the core 50 after the glass ribbon 16 is formed. During molding, heat is removed from the glass due to rapid heat conduction, so it is difficult to avoid the formation of cold wrinkles 52. Other defects may also occur, such as pressure checks (ie, cracks) and scratches.

The method 10 also includes passing 54 the glass ribbon 16 in close proximity to the first elevated temperature zone 56 . In the first heating zone 56, a heat flux is applied to the first major surface 18 of the glass ribbon 16 to a temperature sufficient to cause liquefaction of the composition of the glass ribbon 16 at the first major surface 18. The temperature of the first main surface 18 is increased. This means that the viscosity from the first major surface 18 of the glass ribbon 16 to a depth of at least 100 μm (eg, 100 μm to 500 μm, etc.) in the direction of the thickness 26 is less than or equal to 10 ⁵ poise, such as 10 ⁴ poise or 10 ³ poise. This may correspond to a value on the order of ~10 ⁵ poise. However, the thickness 26 of the glass ribbon 16, the rate of descent of the glass ribbon 16, and the first elevated temperature zone 56 are all such that the temperature of the core 50 of the glass ribbon 16 remains below the softening temperature of the composition of the glass ribbon 16. It is composed of If the core 50 were to soften, the glass ribbon 16 would become thinner before surface defects are reduced or removed. For example, if the lowering speed of the glass ribbon 16 and the heat flux applied in the first temperature increasing zone 56 are given arbitrarily, by increasing the thickness 26 of the glass ribbon 16, the first temperature increasing zone 56 Thus, it is possible to liquefy the first main surface 18 without causing loss of structural integrity due to softening of the core 50. Alternatively, regarding the heat flux applied in the first heating zone 56, the length of the glass ribbon 16 to which the heat flux is applied may be shortened or the intensity of the heat flux may be reduced so that the heat flux is liquefied at the first main surface 18. It is also possible to reduce the thickness 26 of the glass ribbon 16 so that no softening occurs in the core 50. In embodiments, the thickness 26 of the glass ribbon 16 in the immediate vicinity of the first heated zone 56 is between 3 mm and 5 mm. Note that this thickness 26 refers to an arbitrary thickness 26 measured at an arbitrary position between both side edges 22 and 24.

In the first heating zone 56, liquefaction occurs on the first major surface 18 (and thereby in the direction of the thickness 26 from the first major surface 18) while maintaining the temperature of the core 50 below the softening temperature. The temperature of the first major surface 18 is increased to a temperature sufficient to cause a viscosity reduction to occur. Thereby, in the first temperature increasing zone 56, surface defects can be reduced or removed due to the surface tension of the first main surface 18. In other words, the cold wrinkles 52 that were present on the first main surface 18 until they were in the immediate vicinity of the first temperature increase zone 56 are removed from the first main surface 18 in the immediate vicinity of the first temperature increase zone 56. During liquefaction of 18, it is unobtrusively reduced or eliminated. Therefore, variations in the overall thickness of the glass ribbon 16 are reduced. Moreover, the surface roughness (R _a ) of the first main surface 18 is also reduced. Even if there are pressure cracks or scratches on the glass ribbon 16 before entering the first temperature increasing zone 56, they can be repaired and removed. Other surface defects can also be removed or made less noticeable. As used herein, "total thickness variation" refers to the difference between the minimum and maximum thickness 26. For glass ribbon 16, the minimum and maximum thickness 26 values are for thickness 26 measured along the same horizontally extending line. In the case of the glass plate 12, the overall thickness variation is the difference between the minimum value and the maximum value of the thickness 26 of the entire glass plate 12 in a free state where no clamping pressure is applied.

As mentioned above, the glass ribbon 16 is solidified before entering the first heating zone 56. This corresponds to a viscosity of the glass ribbon 16 of the order of 10 ¹⁰ poise to 10 ¹² poise, for example 10 ¹¹ poise. It is not necessary to cool the glass ribbon 16 below the setting zone of the composition of the glass ribbon 16 where the glass ribbon 16 becomes elastic. In the elastic state, the cross-sectional shape of the glass ribbon 16 is fixed and becomes a characteristic cross-sectional shape of the glass ribbon 16. The glass ribbon 16 may change from this state due to deflection, but is urged back to its original solidified cross-sectional shape by internal stresses. However, in embodiments, the glass ribbon 16 has cooled to a lower temperature than the composition condensation zone by the time it is in close proximity to the first heating zone 56. In fact, in embodiments, the glass ribbon 16 has cooled to ambient temperature by the time it is in close proximity to the first heated zone 56. Nevertheless, in order to minimize stress across the glass ribbon 16, it is beneficial to maintain the temperature of the glass ribbon 16 at a point in the immediate vicinity of the first elevated temperature zone 56 above the annealing temperature of the composition. There are cases where The annealing temperature of the composition is the temperature at which the viscosity of the composition is about 10 ¹³ poise.

In embodiments, this step 54 occurs within a time period of 1 second to 10 seconds. In other words, it takes only 1 to 10 seconds for a given portion of the glass ribbon 16 to pass in close proximity to the first heated zone 56. In embodiments, step 54 takes within a period of 1 second, 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, 10 seconds, or any of these times. This is performed within an arbitrary time (for example, 2 seconds to 9 seconds) within a range of two arbitrary end points. After this period of time has elapsed, the predetermined portion of the glass ribbon 16 has fallen below the first temperature increase zone 56. Note that if the time is shorter than 1 second, the heat flux hitting the first main surface 18 will be insufficient, so the temperature of the first main surface 18 of the glass ribbon 16 is set to a point where liquefaction occurs on the first main surface 18. It is highly likely that it will not be possible to raise the temperature to a sufficient temperature for Therefore, it is considered that surface defects cannot be removed to a visible level. On the other hand, a time longer than 10 seconds is longer than the time necessary for surface defects to be removed due to the surface tension of the liquefied first principal surface 18, so it is not necessary to take a time longer than 10 seconds. do not have. Furthermore, if the time exceeds 10 seconds, the risk of softening even the core 50 due to the heat flux hitting the first main surface 18 will increase unnecessarily.

In embodiments, step 54 of method 10 reduces devitrification within glass ribbon 16. Before the glass ribbon 16 passes in close proximity to the first elevated temperature zone 56, the glass ribbon 16 has some degree of devitrification (including devitrification that is continuous to the first major surface 18 of the glass ribbon 16). You may have one. By rapidly heating the first major surface 18 so that sufficient liquefaction occurs on the first major surface 18 and then cooling it, if devitrification exists inside the glass ribbon 16, the devitrification is removed. can be reduced.

In embodiments, increasing the temperature of first major surface 18 in step 54 of method 10 includes directing a flame 58 (see FIG. 7A) at first major surface 18. For example, in one embodiment, a horizontally oriented line burner 60 directs a flame 58 from burning fuel toward the first major surface 18 of the glass ribbon 16, thereby increasing the temperature of the first major surface 18. As a result, liquefaction occurs on the first main surface 18. Note that the line burner 60 is "horizontally oriented" when the line burner 60 has a horizontal width 62 and a vertical height 64, and the horizontal width 62 is horizontally oriented. This means greater than the vertical height 64, for example at least three times greater. In embodiments, the horizontal width 62 is narrower than the width 28 of the glass ribbon 16 facing the line burner 60. In such embodiments, line burner 60 may be centrally located such that line burner 60 does not extend laterally beyond the side edges 22, 24 of glass ribbon 16.

In other embodiments, increasing the temperature of the first major surface 18 to a temperature sufficient for liquefaction to occur at the first major surface 18 includes increasing the temperature of the first major surface 18 to a hot body 66 (see FIG. 7B). ). The high-temperature body 66 transfers heat to the first major surface 18 throughout the first heating zone 56 primarily by thermal radiation 68, although it also causes heat transfer by air convection. In other words, the hot body 66 does not have a turbine that directs the heated gas toward the first major surface 18 of the glass ribbon 16 . Like the line burner 60, the hot body 66 has a width 70 several times greater than its height 72 and can be oriented horizontally. Additionally, the hot body 66 can be centrally located so that the hot body 66 does not extend laterally beyond the side edges 22, 24 of the glass ribbon 16.

Although the line burner 60 and the high temperature body 66 are used to raise the temperature of the first main surface 18 to a temperature sufficient to cause liquefaction on the first main surface 18, this is merely an example. It is not intended to be limiting. The method 10 encompasses any device that causes liquefaction to occur on the first major surface 18.

After the glass ribbon 16 has been lowered and moved out of the immediate vicinity of the first heated zone 56 and has finished reducing the overall thickness variation on the first major surface 18, it is removed from both major surfaces 18, 20 and the core 50. The temperature of the glass ribbon 16 at is approaching equilibrium. That is, the temperature of the core 50 increases and the temperature of the first main surface 18 decreases. As a result, the effective viscosity of the glass ribbon 16 is reduced to the order of 10 ⁶ poise to 10 ⁸ poise, or 10 ⁷ poise. "Effective viscosity" refers to the average viscosity across the horizontal cross-section of the glass ribbon 16. Then, since the effective viscosity of the glass ribbon 16 decreases, the glass ribbon 16 is thinned downward (due to its own weight, tension by a tension roller described later, or both). As a result, the thickness 26 and width 28 of the glass ribbon 16 decrease as a function of downward position. In embodiments, the thickness 26 of the glass ribbon 16 after passing in close proximity to the first elevated temperature zone 56 is at least 1.5 mm.

Conventionally, it has been thought that surface defects can be reduced and removed by thinning without reducing or removing surface defects in advance in step 54. In other words, it was thought that all parts of the glass ribbon 16, including surface defects, would shrink uniformly. However, modeling and experimentation have shown that if the first heating zone 56 is too strong and the temperature of the core 50 rises above the softening temperature of the composition of the glass ribbon 16, surface defects in the glass ribbon 16 may occur. The surprising finding was that the glass ribbon 16 was thinned (i.e., extended downward to reduce its thickness 26 and width 28) without reducing or eliminating the . The thinning of the glass ribbon 16 proceeds preferentially in the thin portions of the glass ribbon 16, for example, in the valleys 74 of the cold wrinkles 52. As a result of such preferential thinning, defects such as the cold wrinkles 52 become worse, and the valleys 74 of the cold wrinkles 52 move closer to the core 50, making the peaks 76 of the cold wrinkles 52 even more conspicuous. This is what happens. In other words, step 54 of method 10 must be performed such that reduction or removal of surface defects due to surface tension occurs before thinning of glass ribbon 16 occurs. Otherwise, the thinning of the glass ribbon 16 will only worsen surface defects.

In embodiments, method 10 further includes passing 78 glass ribbon 16 in close proximity to second elevated temperature zone 80 . The second heating zone 80 is heated to a temperature sufficient to cause liquefaction of the glass ribbon 16 from the second major surface 20 to a depth of at least 100 μm (eg, 100 μm to 500 μm, etc.) in the direction of the thickness 26. The temperature of the main surface 20 of 2 is increased. Note that, as in the case of the first temperature rising zone 56, the thickness 26 of the glass ribbon 16, the descending speed of the glass ribbon 16, and the second temperature rising zone 80 all depend on the temperature of the core 50 of the glass ribbon 16 being It is configured to remain below the softening temperature of the composition of ribbon 16. Thereby, before thinning the glass ribbon 16, surface defects on the second main surface 20 can be repaired by surface tension, and variations in the overall thickness of the glass ribbon 16 can be further reduced. In addition to this, devitrification can also be removed in step 78. Note that the step of increasing the temperature of the second main surface 20 to a temperature sufficient to cause liquefaction on the second main surface 20 may be performed in the same manner as the temperature increase of the first main surface 18 described above. Since it can be done, there is no need to explain it again here. For example, in embodiments, increasing the temperature of second major surface 20 may include directing a flame to second major surface 20, such as by horizontally oriented second line burner 82, or This includes a step of causing the main surface 20 to face the second high temperature body 83 or the like. Except that the second line burner 82 and the second high temperature body 83 oriented in the horizontal direction are arranged to face the second main surface 20 instead of the first main surface 18 of the glass ribbon 16. , the line burner 60 and the high temperature body 66. In either case, after the overall thickness variation of the glass ribbon 16 is reduced and the glass ribbon 16 has descended below the second temperature increase zone 80, the first main surface 18, the second main surface 20 , and the temperature of the core 50 approach equilibrium, the effective viscosity of the glass ribbon 16 decreases, the glass ribbon 16 is thinned, and the thickness 26 of the glass ribbon 16 decreases.

In embodiments, the horizontal planes 85 of the first heating zone 56 and the second heating zone 80 overlap each other. Horizontal plane 85 is a conceptual plane that extends through glass ribbon 16. In such a case, the core 50 remains below the softening temperature while the first major surface 18 and the second major surface 20 are heated to a temperature sufficient to cause liquefaction between the first major surface 18 and the second major surface. The temperature rises at the same time.

In other embodiments, the first temperature increase zone 56 and the second temperature increase zone 80 are staggered in the vertical direction. That is, the first temperature increase zone 56 is arranged at a higher or lower position than the second temperature increase zone 80, and the horizontal planes 85 do not overlap with each other. By staggering the zones 56 and 80 in this manner, surface defects on the first major surface 18 and the second major surface 20 are eliminated during liquefaction of the first major surface 18 and the second major surface 20. It is possible to prevent the glass ribbon 16 from softening to the extent that the core 50 of the glass ribbon 16 begins to thin before it can be removed. However, if the thickness 26 of the glass ribbon 16 is sufficiently thick, there is no need for such a staggered arrangement and both major surfaces 18, 20 can be heated simultaneously. In this case, even if both major surfaces 18 and 20 are heated simultaneously, core 50 will not be softened while surface defects are being removed by causing liquefaction on both major surfaces 18 and 20.

In embodiments, method 10 further includes measuring 84 the thickness 26 of glass ribbon 16. Thickness 26 may be measured with any measurement device 86, such as a device that measures thickness by transmittance of light 88. For example, measurement device 86 may be a confocal chromatic imager. By measuring the thickness 26 of the glass ribbon 16, feedback can be obtained almost in real time, so that the size of the gap 90 between the pair of forming rollers 36a, 36b can be changed, or the flow rate of the flow 38 of the molten glass 32 can be changed. The thickness 26 of the glass ribbon 16 can be adjusted by changing the rotational speed of the pair of forming rollers 36a and 36b. Note that if the surface roughness of the first major surface 18 of the glass ribbon 16 is too large, surface scattering of the transmitted light may occur, but step 54 of the method 10 may, for example, minimize the surface scattering of the transmitted light. Since this can be suppressed to a minimum, the reliability of the measured value in step 84 can be improved.

In embodiments, method 10 further includes pulling 92 down glass ribbon 16 with tension rollers 94 . The tension roller 94 is arranged at a position lower than the first temperature increase zone 56. Tensioning rollers 94 may include a pair of tensioning rollers 94 adjacent first side edge 22 . The tension roller 94 is provided with the tension roller 94 a in contact with the first main surface 18 of the glass ribbon 16 and the tension roller 94 b in contact with the second main surface 20 . Similarly, tension rollers 94 may include a pair of tension rollers 94 adjacent second side edge 24 . The pair of tension rollers 94 are also provided such that one of them is in contact with the first main surface 18 and the other of the pair of tension rollers 94 is in contact with the second main surface 20. In other embodiments, only a pair of tension rollers 94 may be centrally located between the first side edge 22 and the second side edge 24. The pair of tension rollers 94 are also provided such that one of them is in contact with the first main surface 18 and the other of the pair of tension rollers 94 is in contact with the second main surface 20. Tension rollers 94 create a slight tension in the glass ribbon 16 to stabilize the glass ribbon 16 and thin the glass ribbon 16. In embodiments, tension rollers 94 pull the glass ribbon 16 to further reduce the thickness 26 of the glass ribbon 16. The surface material and surface texture of the tension roller 94 must be selected so as not to adversely affect the overall thickness variation of the glass ribbon 16.

The method 10 also includes cutting 96 the glass sheet 12 from the glass ribbon 16. This step 96 occurs after the glass ribbon 16 has moved below the first heating zone 56 and the second heating zone 80 (if included). As mentioned above, glass ribbon 16 is continuously formed until the source of molten glass 32 is exhausted. Therefore, the glass plate 12 can be one of a plurality of 98 glass plates 12 that are sequentially cut from the glass ribbon 16. Step 96 includes any steps used to cut glass sheet 12. In some embodiments, the step of cutting the glass plate 12 includes first drawing a score line on the glass ribbon 16, applying tensile stress across the score line to create a crack, and then creating a crack in the glass ribbon. and propagating the crack through the thickness 26 of 16. Note that the dividing line can be formed by a conventional method. A score line is generated by contacting the glass ribbon 16 with a score member 100 that forms a damage in the first major surface 18 or the second major surface 20, such as a score wheel, scribe, or abrasive member. be able to. Thereafter, tensile stress is applied to the side of the glass ribbon 16 where the score line is attached by bending the glass ribbon 16 in a direction in which tension is applied across the score line. This tension then causes the crack formed at the score line to propagate and penetrate through the thickness 26 of the glass ribbon 16. In addition, it is preferable to form the score line over the quality area of the glass ribbon 16, that is, over the ribbon width 28 between the side edges 22 and 24. The first main surface 18 and the second main surface 20 of the glass ribbon 16 become the first main surface 18 and the second main surface 20 of the glass plate 12.

In other embodiments, the scoring member 100 is a laser, and optionally a laser and a cooling device. The cooling device contacts the glass ribbon 16 with a cooling fluid, such as a cooled gas, liquid, or a combination thereof (mist). The laser heats the glass ribbon 16 across the intended scoring path with the laser beam striking a narrow area of the glass ribbon and heating that area. Thereafter, by cooling the heated path with a cooling fluid, a large tension is created in the glass ribbon 16 and a secant line is generated.

In embodiments, the surface roughness (R _a ) of the first major surface 18 before step 54 of method 10 (or if step 54 is not performed) is greater than 1000 nm, such as from 1000 nm to 5000 nm. On the other hand, the surface roughness (R _a ) of the first major surface 18 of the glass plate 12 after step 54 of method 10 is less than 500 nm, such as between 50 nm and 500 nm, between 50 nm and 250 nm, or between 100 nm and 200 nm. be. Surface roughness (R _a ) is obtained by recording the height deviation 102 of the cross-sectional shape from the average height line 104 at multiple locations in the evaluation target length 106 and taking the arithmetic average of the absolute values of the records. (See Figure 5). In fact, the surface roughness (R a ) of the first major surface 18 before step 54 (or when step 54 is not performed) is such that the surface roughness (R _a ) of the first major surface 18 is such that a portion of the glass ribbon 16 is This can be confirmed by preventing the glass from passing in the immediate vicinity (for example, by letting it pass with the heat flux stopped) and then measuring the surface roughness (R _a ) of the glass plate 12 cut from this area. The surface roughness (R _a ) of the first main surface 18 after step 54 is determined by passing a portion of the glass ribbon 16 in the immediate vicinity of the first heating zone 56 and then cutting it from this portion. This can be confirmed by measuring the surface roughness (R _a ) of the glass plate 12.

In embodiments, the overall thickness variation of the glass ribbon 16 and/or the glass plate 12 cut from the glass ribbon 16 before step 54 of method 10 (or without steps 54 and 78) is 5 μm or more. , for example, from 5 μm to 20 μm. In embodiments, by performing steps 54 and 78, the overall thickness variation of the glass ribbon 16 and the glass plate 12 cut from the glass ribbon 16 is less than 5 μm, such as from 0.5 μm to 4.9 μm. . As described above, the overall thickness variation of the glass ribbon 16 is maintained smaller than desired even after passing through the mold 34 and the cooling wrinkles 52, so that the glass ribbon 16 can be made with smaller overall thickness variation than desired. Ribbon 16 can be formed. Step 54 of passing the glass ribbon 16 in the immediate vicinity of the first heated zone 56 and step 78 of passing the glass ribbon 16 in the immediate vicinity of the second heated zone 80 of the method 10 (but including step 78 case), the overall thickness variation of the glass ribbon 16 is reduced. Thereafter, as the temperature of the core 50 rises and equilibrates with the temperature of the main surfaces 18 and 20, the glass ribbon 16 becomes thinner and thinner, and the overall thickness variation of the glass ribbon 16 is further reduced. Accordingly, the glass sheets 12 cut from the glass ribbon 16 in step 96 have a desirable overall thickness variation of less than 5 μm.

In embodiments, the overall thickness variation of glass sheet 12 formed by method 10 is 50% of the overall thickness variation of glass ribbon 16 before step 54 (and step 78, if included) of method 10. % or less (for example, 10% to 50%). In embodiments, the overall thickness variation of glass sheets 12 formed by method 10 is less than or equal to 50% (e.g., 10% to 50%). For example, the overall thickness variation of the glass ribbon 16 before step 54 (and step 78, if included) may be 8 μm, in which case after step 54 and optionally step 78 The overall thickness variation of the glass plate 12 cut from this glass ribbon 16 is 4 μm or less.

Steps 54 and 78 not only reduce variations in the overall thickness of glass plate 12, but also improve the strength of glass plate 12, compared to the case where steps 54 and 78 are not performed. If Steps 54 and 56 of Method 10 were not performed, surface defects such as scratches and pressure cracks that existed on the formed glass ribbon 16 would have remained on the glass plate 12 cut from the glass ribbon 16. . Steps 54 and 78 reduce and eliminate such surface defects, resulting in a glass sheet 12 with optimal strength.

Glass plate 12 has a width 108 between side edges 22,24. The width 108 inherits the width of the glass ribbon 16 as it is. Further, the glass plate 12 has a length 110. This length 110 is generally perpendicular to the side edges 22, 24 and parallel to the vertical portion of the glass ribbon 16 from which the cut glass sheets 12 are made. Note that all the glass plates 12 cut from the glass ribbon 16 do not need to have the same width 108 or the same length 110. In embodiments, the width 108 of the glass plate 12 is between 5 mm and 500 mm, and the length 110 is between 5 mm and 500 mm. In other embodiments, width 108 is greater than 500 mm and length 110 is greater than 500 mm.

As described above, the composition of the glass ribbon 16 is directly transferred to the glass plate 12. Method 10 can be utilized with any glass composition. In several embodiments, the composition is such that the refractive index of the glass plate 12 cut from the glass ribbon 16 (refractive index for wavelengths of 589 nm to 633 nm at a temperature of 20° C. to 25° C.) is 1.75 to 2.5. be taken as a thing. In other embodiments, the refractive index of glass plate 12 is between 1.45 and 1.75. For example, 40.1 mol% _SiO2 , 11.3 mol% _Li2O , 3.8 mol% _ZrO2 , 4.8 mol% _Nb2O5 , 2.4 _mol % of B ₂ O ₃ , 22.9 mol % CaO , 5.4 mol % La ₂ O ₃ , and 9.3 mol % TiO ₂ has a refractive index (at a wavelength of 633 nm) of The ratio becomes 1.8. In weight %, the composition contains 28.5 weight % SiO ₂ , 4.00 weight % Li ₂ O, 5.5 weight % ZrO ₂ , 15 weight % Nb ₂ O ₅ , It contains 2.0% by mass of _B2O3 , 15.2% by mass of CaO, 21% by _{mass of La2O3} , and 8.8% by mass of _TiO2 .

In some embodiments, the glass composition (in weight percent based on oxides, with total weight percent being 100%)
5 to 55% by mass of SiO ₂ ;
5 to 10% by mass of ZrO ₂ and
3.5 to 18% by mass of CaO,
0.2 to 30% by mass of La ₂ O ₃ ;
0.5 to 20% by mass of Nb ₂ O ₅ ;
5-20% by mass of TiO ₂ ,
0 to 0.2% by mass of As ₂ O ₃ ;
0.05 to 0.9% by weight (preferably 0.1 to 0.9% by weight, for example 0.1 to 0.8% by weight) of Er ₂ O ₃ and/or 0.05 to 1% by weight Pr ₂ O ₃ , or 0.05 to 1% by mass of Nd ₂ O ₃ , or 0.05 to 1% by mass of Ho ₂ O ₃ , or 0.05 to 1% by mass of Ce oxide (CeO ₂ ); ,including.

In embodiments, the glass composition (in weight percent based on oxides, with total weight percent being 100%)
5 to 60% by mass of SiO ₂ ;
5 to 10% by mass of ZrO ₂ and
3.5 to 18% by mass of CaO,
0.2 to 30% by mass of La ₂ O ₃ ;
0.5 to 20% by mass of Nb ₂ O ₅ ;
5-20% by mass of TiO ₂ ,
0 to 0.2% by mass of As ₂ O ₃ ;
0.01 to 0.5% by weight (e.g., 0.05 to 0.5% by weight, or 0.1 to 0.5% by weight) of Er ₂ O ₃ ;
2 to 5% by mass of Na ₂ O;
0 to 9% by mass of K ₂ O ₅ ;
1% by mass or less of SrO;
0 to 20% by mass of BaO,
0 to 1% by mass of F;
0 to 20% by mass of B ₂ O ₃ .

Since the refractive index of pure silica is approximately 1.5, transparency can be improved by keeping the amount of SiO ₂ below 55% by mass (for example, 7 to 45% by mass) and adding a dopant with a higher refractive index. It can be made into a high refractive index glass without noticeable coloring. Note that if the amount of SiO ₂ is increased to more than 60%, it is necessary to add a dopant or a component with a higher refractive index, so there is a possibility that the glass will become colored glass instead of transparent glass. According to some embodiments, the total amount of Er ₂ O ₃ , Nd ₂ O ₃ , Ho ₂ O ₃ , Ce oxide, Pr ₂ O ₃ in the glass is less than 1.5% by weight. This contributes to maintaining the transparency of the glass and maintaining high transmittance (transmission) at desired wavelengths. As discussed above, the liquidus viscosity of glass compositions that form relatively high refractive index glasses is so low that a fusion process cannot be utilized to form glass sheet 12 from such compositions.

In embodiments, method 10 includes feeding molten glass 32 to mold 34 and forming glass ribbon 16 to form first heated zone 56 and second heated zone 80 (if included). It is a continuous process in which the process of passing the glass ribbon 16 in the immediate vicinity of the glass ribbon 16 and the process of cutting a plurality of 98 glass plates 12 from the glass ribbon 16 are performed without interruption over a period of many days, even months or years. . In other embodiments, method 10 is a non-continuous batch process in which a predetermined amount of molten glass 32 is delivered to mold 34 to form a limited length of glass ribbon 16; A limited number of glass plates 12 can be cut from the glass plate 12.

Steps 54 and 78 (if included) of method 10 reduce or eliminate surface defects, thereby cutting glass ribbon 16 into glass sheet 12 having acceptable overall thickness variation and surface roughness. However, if these steps are not performed, it will be necessary to reduce the thickness variation of the glass plate 12 through acid etching and/or mechanical grinding and polishing. it is conceivable that. However, the latter method 10 is costly compared to steps 54 and 78 (if included) of method 10. In addition, since there is a risk of glass dust being generated and damage to the inner surface of the glass plate 12 from the main surfaces 18 and 20, mechanical grinding and polishing may eliminate surface defects and thickness variations of the glass plate 12. Attempts to reduce may not be optimal. On the other hand, steps 54 and 78 (if included) of the process avoid the generation of such glass dust and do not cause damage inside the thickness 26, inner than the major surfaces 18, 20. Additionally, steps 54 and 56 (if included) of method 10 are performed as an in-line process prior to cutting glass sheet 12 from glass ribbon 16. On the other hand, acid etching and mechanical grinding/polishing are usually not performed as in-line processes and require moving the glass plate 12 to another station. Also, while step 54 and step 78 (if included) of method 10 are both performed in less than 10 seconds, the acid etch may take many hours. Furthermore, as mentioned above, glass plate 12 can be manufactured in a wide variety of sizes, including lengths 110 of 500 mm or more. Mechanical grinding and polishing wheels are not suitable for grinding and polishing glass plates 12 of such size.

Example 1 - In Example 1, as shown in FIG. 8, a quartz crucible 112 was placed upside down and placed on a cubic glass 114. The cubic glass 114 had cold wrinkles 52 on its upper surface. Glass cube 114 had a composition similar to that described above, including 28.5 weight percent _SiO2 . The refractive index of this glass composition was 1.8. At time t=0, the flame is not directed toward the quartz crucible 112. However, from after t=0 until 90 seconds later (t=90 seconds), the flame of the oxy-gas torch was directed at the quartz crucible 112, and as a result, the temperature of the quartz crucible increased. The heat from the quartz crucible 112 was then radiated to the glass 114. During this 90 second period, the heat radiated from the quartz crucible 112 increases the temperature of the top surface of the glass cube 114 to a temperature sufficient to cause liquefaction to a certain depth from the top surface of the glass cube 114; Due to the surface tension generated on the upper surface, the cold wrinkles 52 that had existed up until then were removed. Cold wrinkles 52 can be seen in the figure of the cubic glass 114 at t=0 seconds and in the figure at t=55 seconds. On the other hand, in the diagram of the cubic glass 114 at t=90 seconds, not only are no cold wrinkles 52 observed, but a smooth surface is also observed. Note that the overall cubic shape of the cubic glass 114 was not impaired. This is sufficient to raise the top surface of the glass cube 114 to a temperature sufficient for liquefaction to occur at the top surface for a sufficient time to remove the cold wrinkles 52, but the core of the glass cube 114 is , indicating that a heat flux that would not heat the composition to a temperature higher than its softening point could be applied to the top surface of the glass cube 114 by radiation heating.

Example 2 - In Example 2, molten glass having the same composition as the cubic glass of Example 1 was fed into a nip between a pair of forming rollers. The contact surfaces of the pair of forming rollers to the glass were kept at a high temperature. Further, the pair of forming rollers was set to rotate at 0.25 meters per minute. After forming a glass ribbon from the molten glass sent to the rollers by a pair of forming rollers, a horizontally oriented flame burner directs a flame toward the first main surface of the glass ribbon throughout the first heating zone. Ta. A horizontally oriented flame burner was centered across the glass ribbon and had a width narrower than the width of the glass ribbon facing the flame burner. The second main surface of the glass ribbon was not heated. That is, the second temperature increasing zone was not provided. In addition, a pair of centrally located tension rollers pulled the glass ribbon downward to further thin the glass ribbon after passing close to the flame burner. The temperature measurement results of the glass ribbon using infrared rays are shown in FIG.

Glass plates were cut from this glass ribbon. Using a coordinate measuring machine, we measured the surface texture of the first main surface that passed in the immediate vicinity of the first temperature increase zone and the surface texture of the second main surface that did not pass in the immediate vicinity of such temperature increase zone. The surface properties were measured. The measurement results are shown in the graph of FIG. "Distance down the glass plate (mm)" means the distance along the length of the glass plate. The results for the second main surface revealed that the height of the surface repeatedly undulates. This is probably due to cold wrinkles. Although some peak heights were close to 7 μm, most were within the range of 3 μm to 5 μm. In contrast, the results for the first major surface passing in close proximity to the flame burner show a more constant surface texture with a height of about 1 μm or slightly less. The reason why the surface quality is high in the downward distance of the glass plate in the range of 4 mm to 5 mm is probably due to dust adhering to the glass ribbon when the previous glass plate was cut into pieces.

に従うこと、なお式中、μの単位はポアズ、Ａ＝－５．７５、Ｂ＝５６０１．９、Ｔ_０＝３１２．３、Ｔはガラスリボンの温度（℃）とする、（６）ガラスリボンは１．０Ｗ／（ｍ・Ｋ）の熱伝導率を有すること、（６）仮想的に設けられた第１の昇温ゾーンからの熱流束はガウス分布をとり、ベースライン電力密度は３＊１０^５Ｗ／ｍ^２であること、（７）１／ｅレベルでの半値幅は１５ｍｍとすること。また、本モデルでは、ガラスリボンの第１の主面の温度変化とガラスリボンの細薄化係数（attenuation coefficient）を、時間の関数と見なした。細薄化係数は、開始時のガラスリボンの厚さに対するある特定の時間におけるガラスリボンの厚さの比である。モデリング結果を図１１及び図１２のグラフに示す。図１１のグラフには、ガラスリボンの細薄化が始まる前、すなわち細薄化係数が低下し始める前に、第１の主面で液化が生じるのに十分な温度まで、第１の主面の温度が大きく上昇し得ることが示されている。数秒ではあるが、この時間によって、ガラスリボンの細薄化が始まる前に、表面張力により第１の主面の表面欠陥を低減又は除去することができる。 Example 3 - Example 3 involved computer modeling. Modeling was performed based on the following assumptions. (1) The flow rate is 60 pounds (approximately 27.2 kg)/hour, and the width of the glass ribbon is 150 mm. (2) The heat in the glass ribbon is transferred by convection with a heat transfer rate of 5 W/(m ^{2 ·} K). (3) The gray body approximation is performed under the condition that there is no radiation from the participating media. (4) The ambient temperature is a predetermined temperature between 650°C and 20°C. (5) The viscosity of the glass ribbon as a function of temperature is expressed by the Vogel-Fulcher-Tammann-Hesse viscosity equation:

( ₆ ) Glass ribbon has a thermal conductivity of 1.0 W/(m・K), (6) the heat flux from the virtually provided first heating zone has a Gaussian distribution, and the baseline power density is 3* (7) The half width at the 1 ^/ e ^level should be 15 mm. In addition, in this model, the temperature change on the first principal surface of the glass ribbon and the attenuation coefficient of the glass ribbon were considered as a function of time. The thinning factor is the ratio of the thickness of the glass ribbon at a particular time to the thickness of the glass ribbon at the beginning. The modeling results are shown in the graphs of FIGS. 11 and 12. The graph of FIG. 11 shows that before thinning of the glass ribbon begins, i.e., before the thinning coefficient begins to decrease, the first major surface is heated to a temperature sufficient for liquefaction to occur on the first major surface. It has been shown that the temperature of can increase significantly. Although only a few seconds, this time allows surface tension to reduce or eliminate surface defects on the first major surface before thinning of the glass ribbon begins.

The graph in Figure 12 shows that during heating, the effective viscosity of the glass ribbon decreases enough for thinning of the glass ribbon to occur (i.e., before the thickness value begins to decrease from 5 mm). The viscosity of the first major surface of the glass ribbon has been shown to decrease from about 10 ¹¹ poise to less than 1000 poise (10 ³ poise). This phenomenon makes it possible to reduce the viscosity of the first principal surface and remove surface defects by surface tension before thinning begins. The time the heat flux is applied to the first major surface is sufficient to reduce the viscosity of the surface to less than 1000 poise, but may cause devitrification or cause the core of the glass ribbon to contact the surface due to conduction or radiation. It is too long to be heated to the same low viscosity.

Comparative Example 4A and Example 4B - In Example 4B, a glass plate was formed according to the method described above using the first heating zone. As described above, in the first temperature increase zone, the temperature of the first major surface of the glass ribbon was increased to a temperature sufficient to cause liquefaction of the glass ribbon on the first major surface. Next, glass plates were cut from the glass ribbon. Comparative Example 4A was conducted without utilizing a configuration such as a first heating zone before cutting the glass plate. The compositions of the glasses of Comparative Example 4A and Example 4B were similar to the compositions described above, so the refractive index was 1.8. Next, the surface roughness (R _a ) of the glass plates of Comparative Example 4A and Example 4B was measured. As shown in the screenshot of FIG. 13A, the surface roughness (R _a ) of the glass plate of Comparative Example 4A was 1598 nm. On the other hand, as shown in the screenshot of FIG. 13B, the surface roughness (R _a ) of the glass plate of Example 4B is 152 nm, which is 90% ((1598-152)/1598=0.905*100 % = 90.5%). Moreover, the value of surface roughness (rms) also decreased significantly from 2049 nm to 185 nm.

Preferred embodiments of the present invention will be described below.

Embodiment 1
A method for manufacturing a glass plate,
(a) forming a descending glass ribbon as a function of time in a vertical orientation, the glass ribbon having a first major surface and a second major surface facing generally opposite directions; a core disposed between the first main surface and the second main surface;
(b) following the descent of the glass ribbon, passing the glass ribbon in close proximity to a first heating zone, the first heating zone maintaining the temperature of the core below its softening temperature; increasing the temperature of the first major surface to a temperature sufficient to cause liquefaction at the first major surface;
(c) cutting a glass plate from the glass ribbon after the glass ribbon has moved below the first heating zone;
method including.

Embodiment 2
2. The method of embodiment 1, wherein in step (b), the viscosity of the first major surface is reduced and the overall thickness variation of the glass ribbon is reduced.

Embodiment 3
Between step (b) and step (c), after the overall thickness variation is reduced, the temperature of the first principal surface and the temperature of the core approach equilibrium, and the effective 3. The method of embodiment 2, wherein the viscosity is reduced and the thickness of the glass ribbon is reduced.

Embodiment 4
prior to step (a), further comprising directing the molten glass into a nip between a pair of opposing forming rollers;
According to embodiment 1, the step of forming the glass ribbon in the vertical direction includes rotating the pair of forming rollers to roll the molten glass sent to the nip into the glass ribbon. the method of.

Embodiment 5
2. The method of embodiment 1, further comprising pulling the glass ribbon down with a tension roller after step (b) and before step (c).

Embodiment 6
6. The method of embodiment 5, wherein the step of pulling the glass ribbon with the tension roller reduces the thickness of the glass ribbon between the first major surface and the second major surface.

Embodiment 7
Embodiment 1, further comprising measuring the thickness of the glass ribbon between the first major surface and the second major surface after step (b) and before step (c). Method described.

Embodiment 8
The method according to Embodiment 1, wherein the first main surface of the cut glass plate has a surface roughness (R _a ) of less than 500 nm.

Embodiment 9
The method of embodiment 1, wherein the glass plate cut from the glass ribbon has an overall thickness variation of less than 5 μm.

Embodiment 10
The method according to embodiment 1, wherein the overall thickness variation of the glass plate cut from the glass ribbon is 50% or less of the overall thickness variation of the glass ribbon before step (b).

Embodiment 11
In embodiment 1, the thickness of the glass ribbon between the first main surface and the second main surface after step (a) and before step (b) is 3 mm to 5 mm. Method described.

Embodiment 12
2. The method of embodiment 1, wherein the thickness of the glass ribbon between the first major surface and the second major surface after step (b) is at least 1.5 mm.

Embodiment 13
2. The method of embodiment 1, wherein between step (b) and step (c), the thickness of the glass ribbon between the first major surface and the second major surface is decreased.

Embodiment 14
2. The method of embodiment 1, wherein increasing the temperature of the first major surface includes directing a flame at the first major surface.

Embodiment 15
directing the flame toward the first major surface is performed by a horizontally directed line burner;
15. The method of embodiment 14, wherein the horizontal width of the horizontally oriented line burner is narrower than the horizontal width of the glass ribbon facing the horizontally oriented line burner.

Embodiment 16
Embodiment 1, wherein the step of increasing the temperature of the first main surface includes the step of causing the first main surface to face a high temperature body that transfers heat to the first main surface mainly by thermal radiation. The method described in.

Embodiment 17
2. The method of embodiment 1, wherein step (b) reduces devitrification within the glass ribbon.

Embodiment 18
before step (b), the viscosity of the glass ribbon is between 10 ¹⁰ poise and 10 ¹² poise;
In step (b), the viscosity of the first main surface of the glass ribbon from the first main surface to a depth of at least 100 μm in the thickness direction of the glass ribbon is reduced to 10 ⁵ poise or less;
The method of embodiment 1, wherein before step (c), the viscosity of the glass ribbon is increased to between 10 ⁶ poise and 10 ⁸ poise.

Embodiment 19
The method of embodiment 1, wherein step (b) is performed within a time period of 1 second to 10 seconds.

Embodiment 20
The method according to embodiment 1, wherein the glass plate has a refractive index of 1.75 to 2.5 for a wavelength of 589 nm to 633 nm at a temperature of 20° C. to 25° C.

Embodiment 21
A method for manufacturing a glass plate,
(a) forming a descending glass ribbon as a function of time in a vertical orientation, the glass ribbon having a first major surface and a second major surface facing generally opposite directions; a core disposed between the first main surface and the second main surface;
(b) as the glass ribbon is lowered, (i) the temperature of the first major surface is increased to a temperature sufficient for liquefaction to occur at the first major surface while maintaining the temperature of the core below the softening temperature; (ii) a second heating zone that raises the temperature of the second main surface to the liquidus temperature while maintaining the temperature of the core below the softening temperature; passing the glass ribbon in close proximity;
(c) cutting a glass plate from the glass ribbon after the glass ribbon has moved below the first temperature increase zone and the second temperature increase zone;
method including.

Embodiment 22
22. The method of embodiment 21, wherein the first temperature increase zone and the second temperature increase zone are vertically staggered.

Embodiment 23
22. The method of embodiment 21, wherein horizontal planes of the first heating zone and the second heating zone overlap each other.

Embodiment 24
The method of embodiment 21, wherein in step (b), the viscosity of the first major surface is decreased, the viscosity of the second major surface is decreased, and overall thickness variation of the glass ribbon is reduced. .

Embodiment 25
Between step (b) and step (c), after the overall thickness variation of the glass ribbon is reduced, the temperature of the first main surface, the second main surface, and the core is 22. The method of embodiment 21, wherein the glass ribbon approaches equilibrium, the effective viscosity of the glass ribbon decreases, and the glass ribbon thickness decreases.

12 Glass plate 16 Glass ribbon 18 First main surface 20 Second main surface 22 First side edge 24 Second side edge 26 Glass ribbon thickness 28 Glass ribbon width 32 Molten glass 34 Molds 36a, 36b Forming roller 38 Flow 40 Nip 42 Slot openings 44a, 44b Forming roller rotation axis 46 Reservoir 50 Core 52 Cold wrinkles 56 First heating zone 58 Flame 60 Line burner 62 Line burner width 64 Line burner height 66 High temperature Body 68 Heat radiation 70 Width of high temperature body 72 Height of high temperature body 74 Valley of cold wrinkles 76 Mountain of cold wrinkles 80 Second heating zone 82 Second line burner 83 Second high temperature body 86 Measuring device 88 Light 90 Gap between forming rollers 94, 94a, 94b Tension roller 98 Plural glass plates 100 Score member 108 Width of glass plate 110 Length of glass plate 112 Quartz crucible 114 Cubic glass

Claims (11)

A method for manufacturing a glass plate,
(a) forming a descending glass ribbon as a function of time in a vertical orientation, the glass ribbon having a first major surface and a second major surface facing generally opposite directions; a core disposed between the first main surface and the second main surface;
(b) following the descent of the glass ribbon, passing the glass ribbon in close proximity to a first heating zone, the first heating zone maintaining the temperature of the core below its softening temperature; increasing the temperature of the first major surface to a temperature sufficient to cause liquefaction at the first major surface;
(c) cutting a glass plate from the glass ribbon after the glass ribbon has moved below the first heating zone;
method including. 2. The method of claim 1, wherein in step (b) the viscosity of the first major surface is reduced to reduce overall thickness variation of the glass ribbon. Between step (b) and step (c), after the overall thickness variation is reduced, the temperature of the first principal surface and the temperature of the core approach equilibrium, and the effective 3. The method of claim 2, wherein the viscosity is reduced and the thickness of the glass ribbon is reduced. 2. The method of claim 1, further comprising pulling the glass ribbon down with a tension roller after step (b) and before step (c). 2. The method of claim 1, wherein the step of pulling the glass ribbon with the tension roller reduces the thickness of the glass ribbon between the first major surface and the second major surface. 2. The method of claim 1, wherein the overall thickness variation of the glass plate cut from the glass ribbon is 50% or less of the overall thickness variation of the glass ribbon before step (b). 2. The method of claim 1, wherein between step (b) and step (c), the thickness of the glass ribbon between the first major surface and the second major surface is decreased. 2. The method of claim 1, wherein increasing the temperature of the first major surface includes directing a flame at the first major surface. before step (b), the viscosity of the glass ribbon is between 10 ¹⁰ poise and 10 ¹² poise;
In step (b), the viscosity of the first main surface of the glass ribbon from the first main surface to a depth of at least 100 μm in the thickness direction of the glass ribbon is reduced to 10 ⁵ poise or less;
2. The method of claim 1, wherein before step (c) the viscosity of the glass ribbon is increased to between 10 ⁶ poise and 10 ⁸ poise. A method for manufacturing a glass plate,
(a) forming a descending glass ribbon as a function of time in a vertical orientation, the glass ribbon having a first major surface and a second major surface facing generally opposite directions; a core disposed between the first main surface and the second main surface;
(b) as the glass ribbon is lowered, (i) the temperature of the first major surface is increased to a temperature sufficient for liquefaction to occur at the first major surface while maintaining the temperature of the core below the softening temperature; (ii) a second heating zone that raises the temperature of the second main surface to the liquidus temperature while maintaining the temperature of the core below the softening temperature; passing the glass ribbon in close proximity;
(c) cutting a glass plate from the glass ribbon after the glass ribbon has moved below the first temperature increase zone and the second temperature increase zone;
method including. Between step (b) and step (c), after the overall thickness variation of the glass ribbon is reduced, the temperature of the first main surface, the second main surface, and the core is 11. The method of claim 10, wherein the glass ribbon approaches equilibrium, the effective viscosity of the glass ribbon decreases, and the glass ribbon thickness decreases.

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